Conventionally, a substrate processing apparatus for performing a specific process on a substrate, such as a semiconductor wafer or a glass substrate for a liquid crystal display, which is loaded into a processing chamber has been used in a manufacturing process of, e.g., a semiconductor device. In the substrate processing apparatus, for example, a mounting table is disposed in a processing chamber to mount a substrate thereon, and a showerhead for supplying a processing gas is disposed to face the mounting table such that the processing gas is supplied toward the substrate mounted on the mounting table. Further, the substrate processing apparatus includes a baffle plate (also referred to as an exhaust plate) having a plurality of gas exhaust holes (circular holes, elongated holes, or rectangular holes). The baffle plate is disposed to surround the mounting table. A gas is evacuated from the processing chamber through the gas exhaust holes of the baffle plate.
In the substrate processing apparatus having the above-mentioned configuration, a gas is exhausted from the periphery of the mounting table through the baffle plate disposed around the mounting table. Accordingly, it contributes to uniformly maintain a pressure in the processing chamber and a flow of the processing gas, and to achieve process uniformity on the surface of the substrate. Further, in the substrate processing apparatus for processing a substrate by generating a plasma in a processing chamber, the above-mentioned baffle plate is disposed in the substrate processing apparatus, and a voltage is applied to the baffle plate to prevent the plasma from leaking out of a processing space (see, e.g., Japanese Patent Laid-open Publication No. 2004-6574 and corresponding U.S. Pat. No. 7,109,660).
As described above, conventionally, the baffle plate having a plurality of gas exhaust holes is disposed around the mounting table to achieve the uniformity of gas exhaust from the periphery of the mounting table and the confinement of plasma. However, even when the baffle plate is used, the processing gas flows from a central portion of the substrate to a peripheral portion of the substrate in a processing space above the substrate. As a result, a processing speed at the peripheral portion of the substrate is lower than that at the central portion of the substrate. That is, process uniformity (in-plane uniformity) is lowered.